We know that towns will have NPC´s which can be hired, if available, to do certain things... e.g. as guards, as a blacksmith etc.

As for guard towers... well we don´t really know what "town buildings" are currently planned, but I guess you can expect something like this to actually show up. I think especially on Syndesia we can expect buildings that will help defend a town against demons.

Jacopo mentioned there will be "npc shops, defensive structures and other structures of this kind" in this Q&A

@Eurav Right around the 8min. mark is when he addresses the NPC guards (sentinels) and defensive infrastructure (walls).@VyrVandalous I'm just going to make an assumption. Because walls exist, there are most likely going to be towers. However, it does sound like you can station guards on walls. Being that is the case, I would assume if towers exist there would be an advantage, such as a greater field of vision.